An example of a kit includes a flow cell and a cleavage mix. An example flow cell includes a substrate; a catalytic polymeric hydrogel on the substrate, the catalytic polymeric hydrogel including a deblocking catalyst; and an amplification primer attached to the catalytic polymeric hydrogel. The deblocking catalyst accelerates cleavage of a blocking group of a 3′ OH blocked nucleotide introduced to the flow cell and incorporated into a template strand attached to the amplification primer. An example of the cleavage mix includes a component to initiate cleavage of the blocking group.